Ultrasonic instruments, including both hollow core and solid core instruments, are used for the safe and effective treatment of many medical conditions. Ultrasonic instruments, and particularly solid core ultrasonic instruments, are advantageous because they may be used to cut and/or coagulate organic tissue using energy in the form of mechanical vibrations transmitted to a surgical end effector at ultrasonic frequencies. Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels and using a suitable end effector, may be used to cut, dissect, elevate or cauterize tissue or to separate muscle tissue off bone. Ultrasonic instruments utilizing solid core technology are particularly advantageous because of the amount of ultrasonic energy that may be transmitted from the ultrasonic transducer, through a waveguide, to the surgical end effector. Such instruments may be used for open procedures or minimally invasive procedures, such as endoscopic or laparoscopic procedures, wherein the end effector is passed through a trocar to reach the surgical site.
Activating or exciting the end effector (e.g., cutting blade) of such instruments at ultrasonic frequencies induces longitudinal vibratory movement that generates localized heat within adjacent tissue, facilitating both cutting and coagulation. Because of the nature of ultrasonic instruments, a particular ultrasonically actuated end effector may be designed to perform numerous functions, including, for example, cutting and coagulation.
Ultrasonic vibration is induced in the surgical end effector by electrically exciting a transducer, for example. The transducer may be constructed of one or more piezoelectric or magnetostrictive elements in the instrument hand piece. Vibrations generated by the transducer section are transmitted to the surgical end effector via an ultrasonic waveguide extending from the transducer section to the surgical end effector. The waveguides and end effectors are designed to resonate at the same frequency as the transducer. Therefore, when an end effector is attached to a transducer the overall system frequency is the same frequency as the transducer itself.
The amplitude of the longitudinal ultrasonic vibration at the tip, d, of the end effector behaves as a simple sinusoid at the resonant frequency as given by:d=A sin(ωt)where:    ω=the radian frequency which equals 2π times the cyclic frequency, f; and    A=the zero-to-peak amplitude.The longitudinal excursion is defined as the peak-to-peak (p-t-p) amplitude, which is just twice the amplitude of the sine wave or 2A.
The shape of an ultrasonic surgical blade or end-effector used in an ultrasonic surgical instrument can define at least four important aspects of the instrument. These are: (1) the visibility of the end-effector and its relative position in the surgical field, (2) the ability of the end-effector to access or approach targeted tissue, (3) the manner in which ultrasonic energy is coupled to tissue for cutting and coagulation, and (4) the manner in which tissue can be manipulated with the ultrasonically inactive end-effector. It would be advantageous to provide an improved ultrasonic surgical instrument blade or end-effector optimizing at least these four aspects of the instrument.
However, as features are added to an ultrasonic surgical instrument blade to achieve the above-listed aspects, the shape of the blade is typically altered which creates asymmetries therein and causes the blade to become unbalanced, meaning that the blade can have the tendency to vibrate in directions other than the longitudinal direction along the length of the instrument, such as transverse directions. Substantial transverse motion in the blade and/or waveguide may lead to excess heat generation and/or premature stress failure therein. Long, thin ultrasonic waveguides, such as those used in instruments for minimally invasive surgery, are particularly susceptible to transverse vibrations introduced by imbalances, or asymmetries, in the end effector.
U.S. Pat. No. 6,283,981, which issued on Sep. 4, 2001 and is entitled METHOD OF BALANCING ASYMMETRIC ULTRASONIC SURGICAL BLADES, U.S. Pat. No. 6,309,400, which issued on Oct. 30, 2001 and is entitled CURVED ULTRASONIC BLADE HAVING A TRAPEZOIDAL CROSS SECTION, and U.S. Pat. No. 6,436,115, which issued on Aug. 20, 2002 and is entitled BALANCED ULTRASONIC BLADE INCLUDING A PLURALITY OF BALANCE ASYMMETRIES, the disclosures of which are hereby incorporated by reference herein, address balancing blades having asymmetries within a treatment portion of the blade by utilizing asymmetries within an adjacent balance portion. While such approaches have proven eminently successful, there are some applications where balancing may be desirable within the treatment, or functional, portion of a blade.
Solid core ultrasonic surgical instruments may be divided into two types, single element end effector devices and multiple-element end effector. Single element end effector devices include instruments such as scalpels, and ball coagulators. Single-element end effector instruments have limited ability to apply blade-to-tissue pressure when the tissue is soft and loosely supported. Substantial pressure may be necessary to effectively couple ultrasonic energy to the tissue. This inability to grasp the tissue results in a further inability to fully coapt tissue surfaces while applying ultrasonic energy, leading to less-than-desired hemostasis and tissue joining. The use of multiple-element end effectors such as clamping coagulators includes a mechanism to press tissue against an ultrasonic blade that can overcome these deficiencies.
Ultrasonic clamp coagulators provide an improved ultrasonic surgical instrument for cutting/coagulating tissue, particularly loose and unsupported tissue, wherein the ultrasonic blade is employed in conjunction with a clamp for applying a compressive or biasing force to the tissue, whereby faster coagulation and cutting of the tissue, with less attenuation of blade motion, are achieved.
Surgical elevators are instruments used to help facilitate the elevation and removal of soft tissue during surgery. Surgical elevators are generally employed to separate muscle from bone. Cobb or curette type surgical elevators and used in spine surgery, especially to assist in posterior access in removing muscle tissue from bone. To remove muscle tissue from bone using conventional surgical elevators, the surgeon must exert a significant amount of force. This may cause premature fatigue. Also, using significant force on a conventional surgical elevator during this technique may increase the likelihood of error and unwanted tissue damage.
It would be desirable to provide an ultrasonic instrument comprising a surgical elevator blade to remove soft tissue such as muscle from bone and to perform additional surgical functions as well. Also, because ultrasonic frequencies induce longitudinal vibratory movements and generate localized heat within adjacent tissue it would be desirable to provide a protective material for the surgical elevator of such ultrasonic instrument. The protective material may reduce the possibility of blade breakage when in contact with bone or metal retractors and may decrease thermal spread from the back edge of the blade.